"Much of the time people tend to associate soils with agriculture. I'm saying it has much more profound impacts than just that," says Pepper, who specialises in soils, water, and waste management and re-use.

Since the discovery of penicillin, the "mining" of soil for useful organisms has come a long way, he adds.

Only 1%, or less, of microbes can be cultured, but many more natural products can be identified with "genome mining", which can be used to identify potentially useful DNA sequences in soil, says Pepper.

He says soil also keeps pathogens from animal waste out of groundwater.

"The soil can act as a natural filter, it can kill off pathogens, it can biodegrade organics and do a wonderful job of protecting groundwater," says Pepper.

He says one study estimates the soil is by far Earth's most valuable ecosystem, worth around US$20 trillion (A$22.7 trillion).

But this is likely to be an underestimate by several orders of magnitude, says Pepper.

"Indeed life on Earth, without earth, would be impossible," he says.

Big proviso

Pepper says the benefits of soil will outweigh its risks, as long as we don't abuse the soil, and take care to avoid its hidden dangers.

He says naturally occurring dangerous bugs in soil, such as Bacillus anthracis (anthrax), legionella and clostridium, are generally low risk and precautions can be taken to avoid contact with them.

Pepper emphasises it is important to look after the soil itself so that it can keep up its ability to kill off introduced pathogens like E. coli and cryptosporidium present in animal and human waste.

"The big proviso is that we manage things appropriately - that we maintain soil health so we can protect human health," says Pepper.

He says this means we should avoid overloading the soil with animal waste and avoid intensive farming that depletes soil organic matter, creates acid soils, and kills off soil microbes essential for healthy soil.

"Soil can be a public health threat, it can also be a public health saviour. Which it is, depends upon how careful you are," says Pepper.

He says another precaution is to test groundwater for heavy metals, like arsenic, which occur naturally in soil.

Uncertainty of climate change

Pepper says another way soil can impact on human health is through its impact on climate change.

He says while increasing CO2 levels can boost plant growth and carbon sequestration in the soil, greenhouse gas levels can also increase as soil temperatures rise, increasing microbial activity and respiration.

"That balance is going to determine whether soil will help or hinder global warming," says Pepper, adding: "I'm an optimist."